Question about ObjectOutputStream-Implementation

[Linuxhippy]

Hi there!

I am working on implementing the writeUnshared(Object) method in 
ObjectOutputStream, however the comment-quality is so weak (there aren't 
simply any) and my java-knowledge is weak too, so I only have weak 
understanding of that wonderful code ;-)

I am especially focused on the following lines:
[code]
realOutput.writeByte(TC_OBJECT);
writeObject(osc);

if (replaceDone)
assignNewHandle(replacedObject);
else
assignNewHandle(obj);
[/code]

When are these methods called?
I was able to remove the handle-assigning all over the place, till this 
code-segment. If I commented out the if(replaceDon)-part I got 
ClassCast-Exceptions at deserialization-time.

Any help would be really welcome!

Thank you in advance, lg Clemens